1,2:5,6-Di-O-isopropylidene-3-C-methyl--D-allofuranose

The title carbohydrate, C13H22O6, is a derivative of D-glycose, in which the furanosidic and isopropylidene rings are in twisted conformations. The mean plane of the furanosidic ring makes a dihedral angle of 70.32 (18)° with the mean plane of the fused isopropylidene ring. The methyl groups in the other isopropylidene ring are disordered over two sets of sites, with an occupancy ratio of 0.74 (6):0.26 (6). In the crystal, molecules are linked by O-HO hydrogen bonds into chains with graph-set notation C(5) along [100]. Weak C-HO interactions also occur.

In the crystal packing, molecules are linked by O—H···O hydrogen bonds into
chains with graph-set notation C(5) along [100] (Bernstein et
al., 1995). There are also short C—H···O interactions that form a
C(7) chain motif along [001] direction (Fig. 2).

The reaction for obtaining the title compound was taken under nitrogen in a
tritubulate vessel. To it, 2.64 ml (3.95 mmol) of methyl magnesium bromide 3
M diluted in THF (7.9 mmol, 2 eq) was added. Then, under vigorous
stirring and in a ice bath, 3.96 mmol (1.02 g) diluted in dry THF was poured
into the solution. The reaction took place for 5 h in room temperature. After
finishing the reaction, it was slowly added dropwise 10 ml of distilled water
and 1 g of Celite, filtering the resultant product in a Celite layer. The THF
solvent was removed by heat. The aqueous phase was extracted with
CH2Cl2 (3 × 30 ml) and the product washed with distilled water (3
× 20 ml), dried with MgSO4 anhydrous and the solvent eliminated on a
vacuum rotator evaporator apparatus. The solid was recrystallized in hexane and
the yellow solid product was obtained with 72% yield. (m.p. = 104–105°C) (Bio
et al., 2004).

Fig. 1. Ellipsoid plot representation of the molecular structure of compound I with
displacement ellipsoids drawn at the 30% probability level. Atoms C71A/B
and C72A/B are disordered with fractional occupancies of 0.74 (6):0.26 (6)
for the A and B components, respectively.

Fig. 2. A packing diagram of (I), viewed approximately down the b axis.
Hydrogen-bonds are shown by dashed lines.

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes)
are estimated using the full covariance matrix. The cell e.s.d.'s are taken
into account individually in the estimation of e.s.d.'s in distances, angles
and torsion angles; correlations between e.s.d.'s in cell parameters are only
used when they are defined by crystal symmetry. An approximate (isotropic)
treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s.
planes.